1. Field of the Invention
The present invention relates to a circuiting device, and more particularly to a circuiting device used to connect electrically a fixed member to a movable member, or a movable member to a movable member.
2. Description of the Prior Art
As an example of a circuiting device used to connect electrically a fixed member to a movable member, or a movable member to a movable member, known is a flexible printed circuit board which has electrical wiring disposed on a surface of a flexible insulating material. This flexible printed circuit board can be used in various electronics applications. In one example, such a flexible printed circuit board can be used to connect a magnetic head which performs recording and/or reproducing of information to and/or from a magnetic disc as a recording medium in a magnetic disc unit to external circuits. A supporting structure of a magnetic head in a floppy disc unit is disclosed, for example, in U.S. Pat. Nos. 4,151,573 and 4,379,316.
FIG. 1 shows an outline of an arrangement of a magnetic disc and a magnetic head in a floppy disc unit.
In FIG. 1, reference numerals 3 and 5 denote magnetic heads. The magnetic head 3 disposed on the lower surface of a magnetic disc 1 is supported by an elastic plate 6 provided at an end of a carriage 2. The magnetic head 5 disposed on an upper surface of a magnetic disc 1 is supported elastically on the lower surface of an end of an arm 4. These two heads 3 and 5 sandwich a circular magnetic disc 1. The rotation of the magnetic disc 1 in the direction shown by arrow A causes magnetic gaps in magnetic cores not shown in detail on magnetic heads 3 and 5 to slide on the magnetic disc 1, thereby performing recording and/or reproducing to and/or from the upper and lower surfaces of said magnetic disc 1.
A detailed explanation of an arrangement for connecting such magnetic heads to a conventional flexible printed circuit board will be made with reference to FIGS. 2A-2C.
FIG. 2A is a plan view, FIG. 2B a side view and FIG. 2C a bottom view. These drawings show the arrangement on the side of the magnetic head 3, and the arrangement on the side of the magnetic head 5 is approximately the same as the former arrangement except that it has an upside-down relation with respect thereto.
In these drawings, reference numeral 6 denotes an elastic plate supporting the magnetic head 3. This plate 6 is made of a material such as copper alloy or stainless steel, and in this case the plate 6 is formed into an approximately square shape with both ends or surrounding portions fixed by adhesion to the above-mentioned carriage 2. Furthermore, the magnetic head 3 is assembled on both the upper and lower surfaces of an attachment portion 6A formed in the central portion of the elastic plate 6.
The attachment portion 6A is formed into an approximately square shape by four L-shaped long holes 6B, and is bridged to the circumferential portions of the elastic plate 6 at the respective centers of its four sides by bridge portions 6C between the long holes 6B.
Accordingly, the magnetic head 3 is supported swingably over a specified range around X and Y axes shown in FIG. 2A due to the elasticity of the above-mentioned bridge portions 6C, and movably over a specified range upward and downward in FIG. 2B due to the entire elasticity of the elastic plate 6.
The magnetic head 3 comprises the following members.
Reference numerals 7A and 7B denote front core halves (hereinafter referred to as core halves) in the form of a thin plate. These core halves 7A and 7B are opposed to each other via a magnetic gap G.sub.1 and implanted on both surfaces of the elastic plate 6 with the magnetic gap G.sub.1 on the upper side in a manner that the core halves are inserted through the plate 6 upward and downward. A back core 8 is coupled to the side surface of the lower side portion to complete the arrangement of the magnetic core for recording and/or reproducing. The portion of the core halves 7A and 7B protruding from the elastic plate 6 are sandwiched by mask blocks 10 and 11 which function as a reinforcement member and a slider through spacers 9 and 9, respectively. Furthermore, a coil 12 is wound around a portion of the core half 7A between the elastic plate 6 and the back core 8.
Reference numerals 13A and 13B denote thin-plate core halves like the core halves 7A and 7B, and two sets of the core halves are provided. The core halves 13A and 13B in each of these two sets are opposed to each other via magnetic gaps G.sub.2 and G.sub.2, respectively. The core halves 13A and 13B of these two opposed sets sandwich a spacer 14 which is in line with the core halves 7A and 7B and implanted on both surfaces of the elastic plate 6 adjacent to the core halves 7A and 7B in a manner that the core halves are inserted through the plate 6 upward and downward. A back core 15 is coupled to the lower side of these two core halves 13A and 13B to complete the arrangement of a magnetic core for erasing. The portions of the two sets of cores halves 13A and 13B on the elastic plate 6 are sandwiched by the mask blocks 10 and 11, like the core halves 7A and 7B. Furthermore, a coil 16 is wound around the portion of the core half 13A between the elastic plate 6 and the back core 15.
Reference numeral 17 denotes a flexible printed circuit board as mentioned above, mostly in the form of film carrier tape which carries conductor patterns. This flexible printed circuit board 17 is formed from a material having flexibility, pliability and electrically insulating properties, and is shaped into a substantially I-shape, of which the width of fixed portions 17A and 17C at both ends is greater than the width of an intermediate movable portion 17B. One fixed portion 17A is fixed by a means such as adhesion to the attachment portion 6A of the elastic plate 6 which supports the magnetic head 3, and the other fixed portion 17C is fixed to the carriage 2. The movable portion 17B between the fixed portions 17A and 17C is not attached to the surface of the carriage 2, so that the movable portion 17B can bend and twist freely.
In this manner, the movable portion 17B is movable, and the entire flexible printed circuit board 17 has flexibility and pliability, so that the flexible printed circuit board 17 follows the movement of the attachment portion 6A of the elastic plate 6 without restricting that movement, i.e., without restricting the movement of the magnetic head 3, if the length of the flexible printed circuit board 17 is suitably determined.
As shown in FIG. 2C, a plurality of narrow stripes of conductor patterns 18 are formed by copper foil on the lower surface of the flexible printed circuit board 17. The conductor patterns 18 extend from the fixed portion 17A to the fixed portion 17C, and are formed in a substantially parallel fashion so that they do not contact each other. At an end of the conductor patterns 18 on the fixed portion 17A is formed circular connection portions 18A, and at the other end of the conductor patterns 18 on the fixed portion 17C is formed oblong connecting portions 18B.
The connecting portions 18A are connected respectively to terminals 12A and 16A of the above-mentioned coils 12 and 16 by a conductive connecting material, such as solder. Similarly, the connection portions 18B are connected by a means such as soldering respectively to lead wires 19 that are connected to external circuits. This arrangement connects the magnetic head 3 to the external circuits through the conducting patterns 18.
When performing recording and/or reproducing on a magnetic disc using the arrangement of a magnetic head as described above, the magnetic heads 3 and 5 that are supported movably as described above follow in their movement the oscillation generated in the magnetic disc 1 by its rotation, so that damage to the surface of the magnetic disc 1 is prevented, and recording and/or reproducing is performed smoothly.
If the above-mentioned magnetic heads 3 and 5 swing or move upward and downward, following the oscillation of the magnetic disc 1, the flexible printed circuit board 17 also moves to follow this movement, and the forces acting on the flexible printed circuit board 17 at this time are particularly large at the respective boundaries C and D between the fixed portions 17A and 17C and the movable portion 17B, as shown by dotted lines in FIG. 2C. As a result, there is the possibility that the conducting patterns 18 will become disconnected at these portions.
This disconnection occurs when the connecting portions 18A and 18B are connected to the terminals 12A and 16A of the coils 12 and 16 and to the lead wires 19 of the external circuits. That is, if a connecting material such as solder flows from the connecting portions 18A and 18B over the boundaries C and D into the region of the movable portion 17B, the areas around the boundaries C and D on the conducting patterns 18 lose flexibility due to the adhesion of the connecting material to the patterns 18, so that cracks are likely to occur in the said areas and consequently the conducting patterns 18 are likely to be disconnected.
The flow of the connecting material sometimes causes short-circuits between the conducting patterns. Furthermore, peeling of the conducting patterns 18 can occur easily depending in particular on the manner of soldering.
Consequently, special care must be taken when connecting the connecting portions 18A and 18B to the terminals 12A and 16A and to the leads 19 in order to avoid the above-mentioned overflow of the connecting material and peeling of the conducting patterns, and therefore such connecting works are troublesome and time-consuming.
In order to prevent overflow of a connecting material such as solder, consideration has been given to covering all of the above-mentioned flexible printed circuit board 17 except the connecting portions 18A and 18B of the conducting patterns 18, with polyimide resin or resist. This method, however, damages the flexibility and pliability of the flexible printed circuit board 17, so that the movement of the magnetic head 3 is limited. Therefore, this method cannot be used.
The above problems are not limited to the above-mentioned flexible printed circuit board used in magnetic disc units but are common to all circuiting devices mentioned above, that is, circuiting devices which are used to connect electrically a fixed member to a movable member, or a movable member to a movable member portion.